The present invention relates to a radar antenna arrangement for radar sensors for motor vehicles, which enable a rotation of the antenna characteristics.
A leaky wave antenna arrangement is known from U.S. Pat. No. 5,572,228 and U.S. Pat. No. 621,186, which is realised as a mechanically rotating antenna, whereby it enables a surface-structured drum to be rotated in immediate proximity to a dielectric waveguide. Here, the surface structure of the drum in U.S. Pat. No. 557,228 is structured from individual metal strips, the distance of which changes when the drum is rotated in the area of the dielectric waveguide. As a result, a rotation angle-dependent power decoupling is produced via a so-called leaky wave from the dielectric waveguide. The decoupled power is in each case distributed in the area in the form of irradiation which can be described by an adjusted antenna characteristic, which is referred to below as the lobe, the maximum intensity of which is thus dependant on the respective angle of rotation of the drum. The polarisation of the radiated wave is here oriented in parallel with the metal strips which are present on the drum.
An alternative embodiment of the drum is described in U.S. Pat. No. 621,186. There, the surface structure is formed from individual rows of elements such as elevations and indentations in the drum, with appropriately selected dimensions with reference to their length and width. As a result of a corresponding design, a targeted influencing of the polarisation plane of the radiated lobes is possible. However, due to the structure with individual rows of elements on the drum, a discrete rotation of the lobe results, whereby in contrast, the above-mentioned embodiment also enables a continuous rotation.
The basic principle of the dielectric waveguide which is disturbed by a variable, structured surface for the purpose of radiating a leak wave has already been disclosed in WO 87/01243.
Alongside the above-mentioned restrictions with regard to polarisation and, in the second case, discrete rotation, the dielectric waveguide contained in the arrangement represents a particular difficulty with respect to the practical realisation of the antenna, which must at least be arranged to a high degree of precision (also under ambient influences such as temperature and vibration) over certain lengths, in such a manner that it is freely suspended in immediate proximity to the drum.
In the orthogonal plane to the plane of rotation of the lobe (section plane through the drum and the dielectric guide), a very broad characteristic of the lobe furthermore results due to the geometry of the dielectric guide, which must be bundled by an additional reflector and/or microwave lens. This produces a highly excessive size of the entire antenna arrangement which unacceptable in particular for motor vehicle applications.
The object of the present invention is to provide a radar antenna arrangement which is suitable for use in a radar sensor for motor vehicle applications.